Ramanujan's reference to theta functions, a class of modular forms, and Eulerian forms, which are \(q\) -series similar in shape to \(\omega (q), \nu (q),\)  and \(\phi (q)\) , expressible in terms of \(q\) -hypergeometric series ([1]}, [2]}), indirectly points back to earlier examples of Eulerian modular forms. For example, Dedekind's \(\eta \) -function is an important modular theta function of weight \(1/2\)  which can be expressed in terms of a \(q\) -hypergeometric series as follows:
\(  q^{\frac{1}{24}}\eta ^{-1}(\tau ) = \sum _{n=0}^\infty \frac{q^{n^2}}{(q;q)_n^2},\) 
